This invention relates to a EGR system or a system for use in re-circulating part of exhaust gases to the air intake side for reducing the amount of nitrogen oxide (NOx) which is a harmful component of exhaust gases from an internal combustion engine, and more particularly to a flow rate control mechanism for controlling the flow rates of re-circulating exhaust gases and air to be taken into the engine.
Hitherto, it has been a common practice in the exhaust gas re-circulating system of an internal combustion engine to use a mechanically operating mechanism consisting of a combination of a diaphragm and a valve mechanism for obtaining re-circulating exhaust gases at a flow rate commensurate to the flow rate of intake air. However, such a mechanically operating mechanism meets only a partial success, suffering from disadvantages such as complicated constuction, hence high manufacturing cost and increasing man power, with the accompanying inaccurate operation of a diaphragm resulting from various unfavorable conditions such as vibration and environmental temperature, and thus there remains a reliability problem to be solved.